1. Field of the Invention
This invention relates to mechanical seals, and more particularly to self-energized backup rings for mechanical seals such as o-rings.
2. Description of the Related Art
Mechanical seals are used extensively to join systems or mechanical elements together to prevent leakage, contain pressure, or exclude contamination. O-rings are one of the most commonly used mechanical seals because of their simplicity and reliability. An o-ring is an elastomeric loop having a round (or rounded) cross-section that is designed to fit in a groove or gland in one or more sealing faces. The o-ring is compressed as the sealing faces are urged together, creating a seal at the interface. O-rings may be designed to have different diameters, cross-sectional areas, and cross-sectional shapes for different applications. Similarly, the glands or grooves they reside in may be designed to have different shapes and sizes.
In general, the pressure an o-ring is able to resist is directly related to the clearance gap between the sealing faces. The larger the gap, the less pressure the o-ring is able to resist without the aid of an external support. This is because the o-ring may begin to extrude into the clearance gap and cause damage to the o-ring as pressures are increased above a certain threshold. Various techniques may be used to reduce the o-ring's tendency to extrude, such as decreasing the clearance gap, selecting o-ring materials with an increased modulus of elasticity, or using backup rings to fill the clearance gap and thereby prevent the o-ring from extruding into the gap. Backup rings are a common choice for preventing extrusion and may be used in applications where pressures exceed 1500 psi.
When system pressure exceeds 1500 psi, there are generally two choices for producing an acceptable seal. The first and most costly choice is to maintain very tight machining tolerances on the mating components. The second more economical choice is to provide a backup ring to reduce o-ring extrusion into the clearance gap. This allows the mating components to be machined with normal tolerances.
While advantageous and effective, conventional backup rings may have various shortcomings. For example, some backup rings may be energized by the o-ring, meaning that compressing the o-ring also urges the backup ring into the clearance gap. While effective in some applications, such backup rings may not fill the clearance gap completely, be ineffective to fill larger gaps, or not function adequately at very high pressures. This may allow the o-ring to extrude into any remaining gap or be pinched between the backup ring and the sealing face. Furthermore, it may be difficult to retain current backup rings within the gland, especially in face seal applications. That is, prior to joining the mating surfaces, current backup rings may be easily dislodged from the gland, particularly in face seal applications.
In view of the foregoing, what is needed is an improved backup ring that improves many of the shortcomings of the prior art. Ideally, a backup ring would be self-energized rather than energized by the o-ring. Such a backup ring would also ideally bridge large gaps while still being effective at very high pressures. Further needed is a backup ring that is easily retained within the gland and may also help to retain the o-ring within the gland, particularly in face seal applications. Yet further needed is a backup ring that is effective to seal very high pressures with very little pressure exerted between the sealing faces.